The advantages of this invention are particularly evident and the explanation of its operation is facilitated when the invention is applied to the process of mixing paste for the grids of electric batteries, where it serves the purpose of automatically adding sufficient trim water to reach the desired plasticity. Briefly the process consists of an initial mixing of measured amounts of dry lead oxide, additives such as flock and sometimes expanders, and water, followed by a controlled admission of sulfuric acid with cooling air and water cooled mixer walls helping to keep the temperature below, usually, 155.degree. F. Because water is lost through vaporization during the process, it is difficult to add exactly enough water initially so that the residual water is adequate for the final plasticity desired. Therefore after cooling it is usually necessary to "trim" the mixture with a small amount of additional water. The kind of intensive mixer to which this control has been applied is described in U.S. Pat. No. 3,980,282, entitled "Material Mixing Apparatus," and issued Sept. 14, 1976.
With the exception of the addition of the trim water, it has been possible to automate the process with conventional controls, weighing, measuring, charging, and timing the materials and actuating the necessary machine movements, all without the necessity of an operator being present. However, because there was no automatic control of trim water, this part of the process required the presence of an operator. In addition, as is characteristic of all repetitive manual operations, the success of the correct addition of trim water without overshooting and the time required to trim varies from operator to operator. Through utilization of this invention to add automatically the trim water needed, the complete cycle can now be run without the presence of an operator which was heretofore not possible, an obvious and substantial improvement.